There are many applications for accurate wind profile information. Knowledge of the immediate and prevailing wind patterns is important for studying movement of air pollution and the like, for optimizing fire fighting efforts, for planning aircraft flight patterns to reduce fuel consumption, and for prediction of wind shear and other possibly dangerous wind conditions for flying, as well as for better weather prediction.
Radar systems for wind profiling have been in operation for more than a decade, at a number of locations. See Strauch et al, "The Colorado Wind-Profiling Network", J. Atmospheric and Oceanic Tech., Vol. 1, no. 1, March 1984. The Strauch et al reference discusses in detail the practice of wind profiling and also provides details and examples of a network of five wind profiling radars in the Colorado area. The present invention relates generally to improvement of the understanding of data gathered using this or similar wind profiling radar systems; where details of the method of the invention are not set forth in detail, they are generally as disclosed by Strauch et al.
The basic process for monitoring the velocity of winds in the atmosphere using radar is as follows. Pulses of high-frequency power are directed into selected areas of the sky at regular intervals. Power back-scattered from all manner of reflectors, including birds, aircraft, wires, and foliage, as well as the ground, the sea, buildings, and the like is detected. Various processes are known for separating the components of the total power received according to the various reflectors.
Radar pulses reflected from turbulence in the atmosphere can be detected and discriminated to provide indication of the wind velocity. More specifically, some of the radar power in the pulses is reflected back toward the transmitting antenna by turbulence, that is, by temperature and humidity gradients in the atmosphere. Since the turbulence is distributed randomly throughout the region of the atmosphere illuminated by the transmitted pulses, the back-scattered return signal measured by the radar exhibits rapid fluctuations. By comparison, signals returned from point reflectors such as airplanes, or from ground clutter, that is, reflection from the ground, buildings, power lines, or foliage, are normally sine waves with little randomness.
More specifically, the wind velocity at any particular point in time and space is measured responsive to the Doppler shift of the received reflected electromagnetic radar pulses. The Doppler shift is determined by the difference in frequency between the transmitted and received signals. The difference in frequency is split into two channels, the in-phase or I and quadrature-phase or Q channels. Comparison of these two values allows determination of the wind direction. Typically, a series of I and Q values are sampled to produce a time series 64 samples long. The Fourier transform of this set of samples is then calculated to determine a Doppler spectrum of that set of samples. This process may be repeated 25-100 times, the whole process consuming 15-60 seconds, and the spectra thus generated summed to produce an averaged Doppler signal indicating the average velocity of the wind in that particular region of the atmosphere at that particular time. This process is then repeated at a number of regions of the atmosphere and over a period of time, to generate a complete wind profile. See, e.g., FIG. 10 of the Strauch et al paper.
In copending application Ser. No. 08/470,546, filed Jun. 6, 1995 , the same inventor teaches methods of reducing the relative amplitude of the clutter in radar return signals, that is, relatively emphasizing the return signal from turbulence, and thereby improving the signal-to-clutter ratio of the meteorological return. This in turn leads to more accurate wind profile information. The present invention also relates to improvement in the signal-to-clutter ratio of the radar return from turbulence by reducing the return from clutter.